Access terminals, such as cell phones and personal digital assistants (PDAs), are operable to communicate with radio access networks, such as cellular wireless networks. These access terminals and access networks typically communicate with each other over a radio frequency (RF) air interface according to a wireless protocol such as 1x Evolution Data Optimized (1x Ev-DO), perhaps in conformance with one or more industry specifications such as IS-856, Revision 0, IS-856, Revision A, and IS-856, Revision B. Other wireless protocols may be used as well, such as Code Division Multiple Access (CDMA), Global System for Mobile Communications (GSM), Time Division Multiple Access (TDMA), and/or some other wireless protocol.
Access networks typically provide services such as voice, text messaging (such as Short Message Service (SMS) messaging), and packet-data communication, among others. Access networks typically include a plurality of base stations, each of which provides one or more coverage areas, such as cells and sectors (i.e., individual areas of a cell that allow the cell to carry more calls). When an access terminal is positioned in one of these coverage areas, it can communicate over the air interface with the base station, and in turn over one or more circuit-switched and/or packet-switched signaling and/or transport networks to which the base station provides access.
Access terminals and access networks may conduct communication sessions (e.g. voice calls and data sessions) over a pair of frequencies known as carriers, with a base station of an access network transmitting to an access terminal on one of the frequencies, and the access terminal transmitting to the base station on the other. This is known as frequency division duplex (FDD). A base-station-to-access-terminal communication link is known as the forward-link, while an access-terminal-to-base-station communication link is known as the reverse-link. Each of the base stations may transmit one or more pilot signals to the access terminals in the base station's coverage area via the forward-link. The access terminals may use the pilot signals to determine which base station(s) and/or sector(s) to use to conduct a communication session. The access terminals may transmit one or more access probes via the reverse-link to initiate a communication session.